Means for finishing workpieces of irregular shapes



Nov. 20, 1951 H, D. COE, JR., ET AL 2,575,656

MEANS FOR FINISHING WORKPIECES OF IRREGULAR SHAPES Filed Nov. 26, 1948 WITNESSES: INVENTORS I HorryD.Coe,Jr.und

BY Joseph 8.0ym.

flvw' ATTORNEY Patented Nov. 20, 1951 MEANS FOR EINISHIN G WORKPIECES 0F IRREGULAR SHAPES Harry D. Coe, Jr., and Joseph B. Dym, Pittsburgh, Pa.

Application November 26, .1948, Serial No. 62,102

Our invention .relates to methods and means for grinding, sanding, polishing or otherwise finishing irregularly shaped surfaces of workpieces suchas turbineblades, hardware, streamlined appliance parts, cams, etc.

.In the manufacture of irregularly shaped bodies it has been a problem to accurately obtain the desired or theoretically correct surface. For instance, with turbine blades of irregular contour, the conventional practice has been to forge or cast the material as close as possible to the desired shape and then improve the finish :and correct the shape by hand polishing. The blades are alternately held against an abrasive polishing wheel and checked against profile gages at three points until the desired shape is obtained. This method is not only time consuming, but the attainable accuracy depends only upon the skill and judgment of the operator.

It is an object of our invention to provide methodsand means that afford bringing irregular bodies into the desired shape with any desired degree of accuracy and in considerably less time than heretofore required.

-Another object of the invention is to greatly reduce the skill required for obtaining accurately finished surfaces and to render the accuracy uniform over the whole finished surface. These and other objects of our invention will be apparent from the following description.

In accordance with the invented method, we provide a rigid form block or matrix with an irregular matrix surface that substantially matches the irregular surface to be finished, and we run an abrasive belt with its smooth side over the form block while keeping the belt slack. We further hold the workpiece to be finished on the abrasive side of the running belt against the matrix. surface of -the form block so that, due to the slackness of the belt, the belt .adapts'itself to the irregular matrix surface. In this manner, the workpiece can be accurately finished merely by holding or forcing it toward the formpiece without requiring special skill and within a period of only a small fraction of the time necessary for the above-mentioned conventional method.

If the workpiece surface is deeply concave, the belt is run directly over a correspondingly convex form block with the abrasive side out and so guided that it approaches and leaves the block approximately tangential to the surface at the first and last points of contact respectively. .If the surface of the form block or workpiece is sufflciently conical to give the belt the tendency to 4 Claims. (Cl. 51-141) 2 run off the form block, an auxiliary form block of similar shape is provided in reversed relation to the active form block to correct this tendency.

If the surface to be finished isconvex or a combination of concave and'convex, the abrasive beltis run with no initial, or no appreciable tension and enough slack to adapt itself to the concave matrix surface area of the form block. The larger degree of slack thus required may makeit diihcult to drive the abrasive belt with belt wheels in the ordinary manner. However, the belt can then be forced against the belt wheels to secure the necessary traction. One way of doing this is to use vacuum on the belt wheels to suck and hold the running abrasive belt against the wheels. This vacuum method may lead to objectionable noise. According to another and preferred procedure, we run a drive belt together with the abrasive belt over the wheels and keep both belts in face-t0- face contact over a sufficient length to secure the needed traction so that a portion of theWaEive belt can then run free and slack.

The above-mentioned methods, as well as examples of devices suitable for performing these methods, will be understood fromthe following description of the embodiments illustrated j in the drawing, in which: 7 V

Figure 1 shows diagrammatically a -machine for finishing turbine blades or other workpieces with deeply concave surfaces, v

Fig. 2 shows a top view of the workpiece, abrasive belt and form block of the same machine; and s Fig. 3 is-ja diagrammatical illustration'of another machine especially designedfor finishing convex a slightly convex surface. t The machine illustrated by Figures 1 and 2 is equipped with a drivestand 'l for a belt driving wheel 2 whose shaft 3 has bearings rigidly mounted on the stand. The running directionof the driving wheel 2 is indicated by an arrow 4. A backstand 5 of the machine is equipped with an idler wheel 6 whose shaft 1 is journalled in a link structure 8 pivoted at 9 to the stand 5.. The link structure 8 is biased by a weight It and tends to move the idle wheel 'away from-the driving wheel, thus maintaining the abrasive belt II in sufll'ciently taut condition to secure the necessary traction while permitting the belt to yield and become slack at the place of the form block described presently. 1

A workstand [2 located betwen a driv'estand and backstand carries a belt guiding wheel .I 3 and a form block or matrix I4; The form block is surface has an irregular shape in order to permit finishing the correspondingly irregular surface of a turbine blade or other workpiece in accordance with the above-described method. The machine, according to Fig. 1 is especially designed for finishing workpieces with deeply concave surfaces. In the illustrated embodiment, this surface is assumed to be generally conical so that the form block l4 may cause the abrasive belt II to run off the matrix surface. In order to prevent this, an auxiliary or compensating form block I5 is also mounted on the workstand; The compensating form block has about the same shape as the main form block it, but is arranged in the reverse direction, i. e., the tapering side of its surface points to the other side of the belt and hence compensates for the tendency of the belt to run 03 the form block I4. I

Two guides l6 and H are provided in order to facilitate placing the workpiece I8 in the proper position on the abrasive side of the belt. When the belt is running and the workpiece [8 held on the abrasive belt side against the matrix surface of the form block I4, the belt assumes sufficient slackness'between the driving wheel and the form block to permit the belt portion at the matrix surface to adapt itself to that surface. As a result, the workpiece surface is finished with the desired accurate shape without requiring special skill and within a period of time much shorter than otherwise required. A water spray nozzle is denoted by 19 and an arrow 20 indicates the feeding direction for the workpiece H3. The arrangement of the form block I4 is preferably such that the belt ll approaches and leaves the block approximately tangential to the matrix and workpiece surface at the first and last point of contact respectively.

The machine illustrated in Fig. 3 has stand 2! for the driving wheel 22. machine of Fig. l, the bearings for the wheel shaft 23 are rigidly mounted on the stand. The driving direction of the wheel is indicated by an arrow 24. A backstand 25 carries an idler wheel 26. The shaft 21 is journalled in a structure 28 that is pivoted at 29 to the stand 25 and biased by a weight 30. The abrasive belt 3| which extends around the drive wheel 22 and idler wheel 26 passes over the matrix surface of a convex form block'34', which is mounted on a workstand 32. The workstand 321s also equipped with guides 36 and 31 for the wo'rkpiece'38 and with a water spray nozzle 39. In order to permit the belt to adapt itself closely'to the concave matrix surface while running over the form block, a larger amount of yielding or slackness is required than with convex matrix surface. Consequently, the traction-of the driving wheel may become insumcient to pull the belt over the form block when the workpiece is fed against the block. In order to secure the necessary traction, the machine according to Fig. 3 is equipped with an auxiliary rubber belt 40. This belt is endless like the abrasive belt, but has greater length so that it lies in face-to-face relation with the abrasive belt on only one side of the wheels but is spaced from the abrasive belt at'the other side. In order to maintain the proper spacing and for. keeping the auxiliary traction belt in taut condition, a pressure roller 4| engages the belt 40. The roller H is journalled on an arm 42 pivoted at 43 to the workstand 32 and secured in the desired position by means of an adjusting screw 44. t

When the. machine is in operation and the a driveworkpiece. 38 vheldon the-. abrasive. side-of belt 3 I As in the 4 against the form block 34, the belt portion between the driving wheel 22 and the form block 34 can run with any suitable degree of slackness without reducing the traction below the required amount.

Methods and means, according to the invention, are applicable with advantage for the finishing of a large variety of irregular surfaces, i. e., of surfaces that are neither plane nor straight cylindrical or straight conical and hence cannot readily be shaped by conventional turning, shaping and grinding devices. Aside from the fact that the invention secures a high accuracy and requires less skill, the fabricating method used for bringing the workpiece surface into approximately the desired shape before finishing need not be so closely controlled as is necessary in the conventional procedure, thus lowering the amount of rejects and further reducing the finishing cost. For example, in machines built and operated according to the inv'e'ntion'for finishing gas turbine blades, the overall savings afforded by the invention in comparison with the conventional methods amounted to approximately The invention also affords a very simple method of forming and redressing the matrix blocks. For such purposes, it is merely necessary to reverse the belt so that its abrasive side runs over the matrix block to be finished or redressed, and to hold a masterworkpiece on the smooth belt side against the matrix block. 3

It will be obvious to those skilled in the art after a study of the present disclosure, that devices according to the invention can be modified as respects various design details and components without departing from the essence and feature of our invention and within the scope of the claims annexed hereto. 1

We claim asour invention: I

l. .A device for finishing a workpiece of irregular shape, comprising two initially spaced belt wheels, an endless abrasive belt having 'a smooth inner surface and an abrasive outer surface and extending around said two wheels, an endless drive belt extending around said two wheels, said drive belt having a portion extending from one 'to the other wheel in face-to-face engagement with said abrasive belt and having another. portion spaced from said abrasive belt, and a form block disposed between said wheels at a place where said driving belt is spaced from said abrasive belt,'said form block having a matrix surface substantially matching'the'surface to be finished and engageable by. said inner surface of said abrasive belt when'a workpiece is held on the outer side of said abrasive belt against said block. 2. A device for finishing a workpiece of irregular shape, comprising two mutually spaced belt wheels, an endlessabrasive belt having a smooth inner surface and an abrasive outer surface and surrounding said two wheels, an endless drive belt having larger length than said abrasive belt and surrounding said wheels and said abrasive belt, tautening means engaging said drive belt to maintain it spaced from said abrasive belt at one side of said wheels and in contact with'said abrasive surface of the other side of said wheels, a. form block having a matrix surface substantially matching the surface to be finished and being engageable by said innersurface of said abrasive belt and disposed at a place wheresaid drive belt is spaced from said abrasive belt.

.3. In a device accordingto claim 2, one of said wheels having a drive shaft and a stationary. axis,

5 said other wheel having an idler shaft movable toward and away from said drive shaft, and biasing means connected with said idler shaft for biasing it away from said drive shaft.

4. A device for finishing a workpiece of irregular shape, comprising two mutually spaced belt wheels, an endless abrasive belt having a smooth inner surface and an abrasive outer surface and surrounding said two wheels, an endless drive belt having larger length than said abrasive belt and surrounding said wheels and said abrasive belt, tautening means engaging said drive belt to maintain it spaced from said abrasive belt at one side of said wheels and incontact with said abrasive surface of the other side of said wheels, and a supporting block having a surface engaged by the inner side of said abrasive belt and being disposed within said abrasive belt at the belt side where said drive belt is spaced from said abrasive belt.

HARRY DEAN COE, JR. JOSEPH B. DYM.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 20 128,321

UNITED STATES PATENTS Name Date Leach Dec. 24, 1895 Fletcher Mar. 20, 1900 Sagerdahl Aug. 8, 1911 McNalley Nov. 9, 1915 Johnson Dec. 24, 1918 Freeman Oct. 31, 1922 Fowler Sept. 29, 1942 Roth et a1 Nov. 23, 1943 Glike May 22, 1945 Clave et a1 Nov. 16, 1948 FOREIGN PATENTS Country Date Germany Feb. 12, 1901 

